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ISSN:!1579*4377!
EFFECTS OF ELECTRON-BEAM IRRADIATION ON
PHYSICOCHEMICAL PROPERTIES OF OIL PALM FROND
BASKETS
Paul Chidozie Onyenekwe*1, Mario Stahl, Ralf Greiner
Max Rubner Institut, Bundesforschungsinstitut für Ernährung und Lebensmittel, Molekularbiologisches
Zentrum, 76131 Karlsruhe, Germany.
pconyenekwe@yahoo.com.
ABSTRACT
Palm frond baskets have been an integral part of packaging in many countries and have
formed part of the local culture such that certain agro products are assumed to be in their
best when packaged in palm frond baskets, hence many resist the use of synthetic materials.
Irradiation of materials requires pre-packaging; there is the need therefore to understand the
effect of irradiation on the biomaterial and determine the possible parameters that can be
used for identification of irradiated materials. The effect of electron beam radiation
treatment on the physicochemical properties of oil palm frond basket was investigated.
Irradiated baskets showed a dose dependent ESR signal intensity and retained more than 13
% of the signal 30 days post-irradiation. Irradiation had no effect on the hygroscopicity.
Headspace analysis showed no significant difference in the composition of the constituents,
however differences in per cent content of 2-methyl-1-penten-3one, 3-methyl-butanal,
decanal, heptanes, 5-hepten-2one and dodecamethyl cyclohexasiloxane were observed. Palm
frond baskets can be used as packaging material for agricultural produce meant for
irradiation and ESR could be used to differentiate irradiated and non-irradiated baskets.
Heptane and 2-Methyl-1-penten-3-one which increased by over 500 times post-irradiation
can be candidates for identification of irradiated baskets.
KEYWORDS
Cellulose, ESR, hygroscopicity, headspace, packaging, radiation.
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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INTRODUCTION
Oil palm (Elaeis guineensis. Jacq) is one of the major cash crops of Nigeria and was the
major foreign exchange earner of the defunct Eastern Nigeria before the discovery of
petroleum. It also grows well in other wet and humid places like Malaysia (Basiron, 2007)
which is now the world highest producer of palm oil (Chew and Bhatia, 2008).
Apart from palm oil and palm kernel oil which are the main articles of trade from oil
palm, other parts such as the trunks, fronds and kernel shells are used in house building and
decorations. The empty fruit bunch is used in soap making, mushroom production and the
fronds used in basket making and fences. With the advent of modern building materials,
basket making has become the main use of the fronds. The major use of these baskets is the
transport of agricultural produce like tomatoes and other horticultural fruits (Adegoroye and
Eniayeju, 1988) and sundry uses like in palm oil production (Taiwo et al, 2000). These fruits
are usually harvested at the climacteric stages while still strong and transported in baskets.
In most developing countries, major losses occur in the post-harvest distribution of
horticultural produce (Holt and Schoorl, 1981). Most losses result from damage caused by
static and dynamic stresses during transit (Olorunda, and Tung, 1985), and by rough
handling during loading and unloading (Dahlenburg, 1983). Although some impact-induced
damage is caused by shocks during transportation, but dropping during container stacking
and destacking is more important (O'Brien, et al. 1965). Comparing cane and oil palm frond
baskets Adegoroye and Enaiyeju (1988), observed that fruits packed in cane baskets were
more susceptible to impact-induced damage of all defect categories than oil palm fronds.
They observed that the total damage was three times greater in cane than in frond
baskets and no visible impact damage was noticed on any of the baskets. Hence fronds have
advantages over cane basket as high tensile and compressive strength materials.
Oil palm frond has been found to be composed of ash 0.70 – 2.4%; lignin 15.2 –
20.5%; holocellulose 82.2 – 83.5%; (Wanrosli, et al. 2005, Abdul Khalil et al. 2006);
cellulose 39.0 – 52.7%; (Wanrosli, et al. 2005, 2007; Sun et al. 2005; Xu et al 2005)
depending on the method of determination and hemicellulose 33% (Fazilah et al. 2009).
Most packaging materials are made of natural or synthetic materials and are often
subjected to ionising radiation when used in packaging of goods that are to be irradiated. The
effect of radiation on these materials is very crucial for the choice of packaging material
based on the intended dose. Palm frond consists of mainly holocellulose and lignin (Abdul
Khalil et al. 2006; Wanrosli, et al. 2007). Although lignin constitutes a small fraction of the
frond, since baskets is made from the frond bark (Soyebo et al. 2005), which is highly
lignified, lignin therefore may constitute a high fraction of the material. The functional
significance of lignin has been associated with the mechanical support (Boudet, 2000).
Lignin has been implicated to play a role in photodegradation of wood (Feist, and
Hon, 1984). Yellowing of lignocellulosic materials and woods surfaces indicates the
modification of lignin and holocellulose. Cellulose undergoes chain scission when irradiated
resulting in a loss in mechanical properties.
The government of Nigeria through its agency, Nigeria Atomic Energy Commission
(NAEC), has recently established an irradiation facility at Abuja. More than one year after
the commissioning of this facility it has been very difficulty getting farmers convinced to
spent extra money to acquire plastic crates and jettison their traditional packaging material.
The aim of the project was to determine the effect of irradiation on the physicochemical
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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properties of oil palm frond basket and propose parameters that can be used to differentiate
irradiated and non irradiated baskets using physicochemicals parameters.
MATERIALS AND METHODS
MATERIALS
Fresh oil palm frond materials were prepared into stripes in making small baskets. These
were allowed to equilibrate with the ambient conditions for two weeks before they were
subjected irradiation.
METHODS
IRRADIATION
The samples were irradiated at ambient conditions at a dose level of 0, 5 and 15 kGy using a
linear accelerator (10 MeV, 10 KW). The dose rate was approximately 107 Gy/s. Irradiation
was carried out in the presence of air at room temperature at the plant of the Beta-Gamma-
Services GmbH & Co KG (Bruchsal, Germany). The dosimetry was carried out by Alanin
dosimeters, the detection methods used were Photostimulated Luminescence Method (PSL)
and Electron Spin Resonance Method (ESR). Irradiated samples were re-irradiated three
weeks and the effect determined.
PHYSICOCHEMICAL ASSESSMENTS
WATER SORPTION ISOTHERM
Water sorption isotherms were determined by the gravimetric method. Samples were stored
in humidity chamber (Tritec®, Hannover Germany). The experiment was carried out at
35oC. Moisture content was calculated on initial-dry weight basis using the equation: M =
(W - Wi/Wi) x 100%
€
M=W−Wi
Wi
#
$
%
&
'
(
x100%
where W and Wi were the weight (g) of the baskets at measured conditions and initial
dry weights respectively.
ESR SPECTROSCOPY
ESR measurements were carried out according to European Standard for the detection of
cellulose radicals using EN 1787 (2001). Palm frond strips fine strips and transferred to 4.0
mm quartz capillary tubes and packed with gentle tapping to a length of 30.0 mm (active
length) in triplicates, and the weight of the sample was determined. The results for the signal
intensity of samples were normalized to the packing weight. ESR measurements were
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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performed using a Bruker Biospin spectrometer (E-Scan, Bruker, Germany). All of the
spectra were recorded at ambient temperature of the ESR laboratory (27°C).
Operating conditions of the ESR spectrometer were as follows: centre field, 3488 G;
sweep width, 180 G; microwave power, 1.653 mW; microwave frequency, 9.808 GHz;
modulation frequency, 86.00 kHz; Mod. Amplitude: 4.60 G; receiver gain, 3.17e+002;
sweep time of 5.243 s and time constant, 40.960 ms.
PSL MEASUREMENTS
The photostimulated luminescence (PSL) measurements were carried out as described by EN
13751 (2002), using a SURRC PPSL Irradiated Food Screening System (SURRC, Glasgow,
United Kingdom). The PSL system (serial; 0021, SURRC; U. K) was used for PSL
measurement of the whole samples (c5 g) placed in a disposable Petri dish with a 50 mm
diameter (Bibby sterlin type 122, Glasgow, U. K). The PSL signal was recorded at a rate of
counts/60 s for both the control and the irradiated samples. The emitted PSL signals (photon
counts, PCs) from the sample per second were automatically integrated in the PC and
presented as counts/60 s. Two PSL signal thresholds, the lower threshold (T1, 700 counts/60
s) and upper threshold (T2, 5000 counts/60 s) were compared. Under this, three classes of
samples are possible namely, positive, intermediate and negative. The intermediate which is
in between the two thresholds requires further investigations to ascertain whether the test
samples have been irradiated or not. Post-irradiation storage and handling of the samples
were carried out in the dark and under yellow light respectively.
EXTRACTION–GC/MS ANALYSIS
The extraction procedure of the samples was carried out as follows: Samples of 1.0 g each
from both control (non-irradiated) and irradiated fronds were cut into small pieces
approximately 0.05 - 0.5 cm.
A Schimadzu GCMS-QP2010 Plus was utilized to obtain chromatograms of the
extract. The separation was performed on a HP-5MS fused silica column (5% phenyl methyl
polysiloxane 30m×0.25mm i.d., film thickness 0.25 µm). The oven was held at 50O C for 2
min during injection then temperature programmed at 5 °C min−1 to a final temperature of
210 O
C and held for 5 min. Injection temperature was kept at 220 O
C all the time. Five-
microliter volume of essential oil was injected into the GC. Helium carrier gas at a constant
flow-rate of 0.68 mLmin−1 and a 5:1 split ratio were used simultaneously. Mass spectrometer
was operated in full scan and standard electronic impact (EI) modes with electron energy of
70 eV. Interface temperature: 280OC; Ion source temperature: 200OC; MS quadruples
temperature: 160OC. In the range of m/z 45–350, mass spectra were recorded with 3.12 s
scan−1 velocity.
RESULTS AND DISCUSSION
The water sorption isotherms at 35 °C of the samples, non-, single dose, and double dose
irradiated samples are shown in figure 1. The isotherms are of the sigmoidal form, which is
type II isotherm. The hygroscopicity of the baskets was not affected by irradiation or re-
irradiation. Although Liu et al. (2005) had observed increased water absorption in
microwave irradiated cellulosic materials due to rapture of the radial parenchyma and some
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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pit membrane which then serve as artificial channels of liquid and gas; our result may be an
indicative of non-disruption of these tissue components of the plant material. This may
explain the observation of Despot et al, (2007), who observed that gamma irradiation of
wood, a cellulosic material, up to 150kGy had no significant effect on the maximum
swelling and total water soluble carbohydrates. Depolarisation of cellulosic materials had
been shown to be more when irradiated in pulp than in wood form (Skvortsov and
.Klimentov, 1986).
Figure 1: Water sorption isotherm at 35oC of the baskets of different doses (R stands for re-irradiated or double
irradiation 22 days after the first irradiation.
ESR SPECTROSCOPY
Non-irradiated palm frond strip exhibited one weak singlet ESR line characterised by g =
2.011±0.0095 centred around 3486 G without any satellite peak (figure 2a). This ESR
spectrum is known to be typical of non-irradiated plant materials. Although the origin of the
free radicals responsible for this spectrum is not well understood, it had been opined to be
semiquinones-like radicals produced by the oxidation of plant polyphenols (Swartz et al
1972) or lignin (Maloney et al 1992; Tabner and Tabner, 1994). Lignin had been shown
(Abdul Khalil et al. 2006, Wanrosli et al.2007) to constitute 15.2 – 20.5% of palm frond and
this may explain the observed ESR signal of the non-irradiated samples. Irradiation of the
palm frond produced more enhanced spectra of the same singlet ESR line with two
symmetric satellite peaks (figure 2 b, c and d) on the left and right of the main peak with a
distance of 60.0G in between them. Hence the frond exhibits cellulose-like ESR spectrum.
The relationship between dose and ESR signal amplitude (satelite peaks) is shown in figure
3. There was no correlation between dose given and the signal amplitude after the first
treatment. The amplitude of the 15 kGy treated sample was 9.5x and 8.1x that of 1 and
5 kGy samples respectively. However re-irradiation of the samples twenty-two days later
gave a linear regression with y = 99957x + 61086 and R2 = 1. Re-irradiation although
0!
2!
4!
6!
8!
10!
12!
14!
16!
18!
70%! 75%! 80%! 85%! 90%! 95%! 100%!
Moisture!Content!(g/100g)!
Relative!Humidity!(%)!
0kGy!
1kGy!
1kGy!R!
5kGy!
5kGy!R!
15kGy!
15kGy!R!
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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significantly (p<0.05) increased the ESR signal amplitude but at 1.29, 3.7 and 1.28 of
magnitude of the corresponding treatments day zero after irradiation respectively.
2a
The non-apparent doubling of the ESR signal amplitude after re-irradiation can be
explained by the reduced level of radicals during storage as shown in figure 3 (Single at 22
days). Earlier Yordanov et al, (2009), have shown that radiation induced ESR spectrum
intensity decays rapidly in the first 30 days post radiation processing, similarly Bayram and
Delince´e, (2004) observed decline of cellulosic radical with extent of storage time after
irradiation, and it had been opined that radicals trapped in the crystalline and semicrystalline
regions of cellulose structures decay through recombination reactions (Khan et al, 2006)
involving the radiolytes with time (Onyenekwe et al 1997). Another possible reason for non-
doubling of the ESR signal amplitude could be saturation effect, as the crystalline and non-
crystalline regions of the cellulosic material may have limited amount of radicals they can
trap and sustain at a given time.
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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2b
2c
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2d
Figure 3: Dose signal intensity relationship
y!=!79181x!+!9178.!
R²!=!0.992!
y!=!8617.x!+!25037!
R²!=!0.995!
y!=!99957x!+!61086!
R²!=!1!
0.00E+00!
2.00E+05!
4.00E+05!
6.00E+05!
8.00E+05!
1.00E+06!
1.20E+06!
1.40E+06!
1.60E+06!
0! 2! 4! 6! 8! 10! 12! 14! 16!
ESR!Signal!Intensity!
Dose!(kGy)!
Single!
Single!
@22days!
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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EFFECT OF STORAGE TIME ON THE ESR SIGNAL AMPLITUDE
There was rapid reduction in ESR signal intensity within the first 10 days post irradiation.
Irradiation of cellulosic materials had been shown (Khan et al 2006) to induce reactions in
the macromolecules through rapid localization of the absorbed energy within the molecules
to produce long- and short-lived free radicals. Radiation-induced radical stability had been
reported to depend not only on the sample and storage conditions but also on the radiation
source (Esteves et al. 1999). They found that the characteristic ``cellulose'' radical observed
in pistachio shells couldn't be recorded after 6 months when electron irradiation was used
while it was still observed for the gamma-irradiated samples whereas in date stones the
cellulose signal disappeared between two to three months post irradiation irrespective of the
radiation source.
PSL Properties
Table 1 shows the results of the PSL photon counts for the electron bean irradiated and non-
irradiated oil palm frond baskets. The photon counts of nonirradiated and up to 5 kGy treated
samples were less than the lower threshold value (700 counts/60 s), indicating a clear
negative. Whereas, the photon counts of the 15 kGy irradiated samples was higher than the
lower threshold value but far below the upper threshold value (5000 counts/60 s), hence can
be classified to be in the intermediate range. The photon count depends to a great extent on
the quantity and type of minerals on the surface of the sample and on the treatment level
(Cutrubinis et al, 2005). The low photon counts of the irradiated samples may be due to its
low mineral content (Wanrosli et al, 2007).
Table 1: PSL mean signal for electron beam irradiated and non-irradiated oil palm fronds
Sample
Terminal Count
Result
0 kGy
516
Negative
1 kGy
574
Negative
5 kGy
627.5
Negative
15 kGy
1725.5
Intermediate
Threshold value: T1= 700; T2 = 5000. (Negative) < T1, T1 < (Intermediate) < T2, and (Positive) > T2.
EFFECT OF TREATMENT ON THE VOLATILE CONSTITUENTS
The headspace analysis of the non-irradiated and the 15 kGy irradiated samples showed the
presence of twenty-six different volatiles out of which twenty were identified. The identified
volatiles were mainly hydrocarbons, aldehydes, ketones and siloxanes. There was no
significant difference in the volatile composition of the irradiated and non-irradiated baskets;
however there was apparent difference in the quantity. Decanal was found to decrease
tremendously from 12.93 % in non-irradiated samples to 1.51 and 1.46 % in 15 kGy and 15
kGy re-irradiated samples respectively. Similarly irradiation led to reduction of 4-
tetradecene from 19.26 % in non-irradiation samples to 1.14 in 15 kGy re-irradiated samples
and trace in 15 kGy samples. Irradiation increased the per cent content of 2-Methyl-1-
Penten-3-one in baskets by more than ten folds. Generally, irradiation increased the per cent
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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content of 5-heptenone, benzaldehyde, heptane and heptanal. These volatiles may cause
sensory changes in (or lead to taint transfer to) packed products (Sajilata et al, 2007).
According to Hollifield (1991) in polyester films that had been metallized with aluminium
laminated either to paperboard or between 2 layers of paper, the more paper, the greater the
amount and number of volatile substances released on heating and at elevated temperatures,
both volatile and non-volatile chemicals from the package can migrate into foods. Lox et al,
(1991) found an increase in migration as a function of dose up to 10 kGy and a decrease at
higher doses from extruded PVC irradiated with 3 to 25 kGy γ –rays; however, with
accelerated electrons, the migration increased steadily with the absorbed dose. The number
of substances released at levels greater than 0.5 µg/inch2 of susceptor surface was found to
include acetone, methyl vinyl ketone, pentanal, toluene, hexanal, furfural, heptanal,
benzaldehyde, nonanal, furan, isobutanol, acetic acid, butanol, octanal, styrene, octyl acetate,
-hydroxymethylfurfural, and crotonaldehyde. 36 Among these volatiles, heptanal and
benzaldehyde, are present in palm oil frond baskets and increased by irradiation dose.
Benzaldehyde had been reported (Chu and Yaylayan, 2008) to be a potent aroma chemical
of bitter almond, that can also be formed thermally from phenylalanine and may contribute
to the formation of off-aroma while heptanal has a strong fruity odour and is used as an
ingredient in cosmetics, perfumes, and flavours.
The result of this work demonstrates that palm frond baskets can be used as
packaging material for agricultural produce meant for irradiation and ESR can be used to
differentiate irradiated and non-irradiated baskets. It was also observed that some volatile
constituents such as Heptane and 2-Methyl-1-penten-3-one which increased by over 500
times post-irradiation can be candidates for identification of irradiated oil palm frond
baskets.
ACKNOWLEDGEMENTS
The first author is a recipient of Resumption fellowship of Alexander von Humboldt
Foundation Bonn Germany and wish to acknowledge the Foundation.
Onyenekwe, P. Ch. et al. EJEAFChe, 9 (6), 2010. [1006-1018]
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Table 2: Retention time and composition of major compounds in the essential oils obtained from control and
electron beam-irradiated oil palm fronda.
Area %
Peak
Component
Retention Time [Rt]
0kGy
15kGy
15kGyR
1
3-Methyl-Butanal
3.050
10.27
1.32
14.53
2
Ni
3.125
2.04
7.15
2.86
3
(E)-2-Hexene
3.333
9.27
8.58
1.75
4
Ni
3.425
9.01
2.45
9.19
5
Ni
3.500
1.75
1.45
2.86
6
Ni
4.158
0.54
4.81
3.08
7
2-Methyl-1-Penten-3-one
4.442
1.27
16.56
19.06
8
1-Octene
4.767
0.66
ND
1.11
9
Hexanal
4.975
2.64
ND
1.23
10
4-Tetradecene
6.300
19.26
ND
1.14
11
Ni
7.350
0.48
2.17
1.56
12
Ni
7.617
0.60
1.32
0.73
13
Heptanal
7.725
1.14
3.44
2.95
14
2,7-dimethyl-Oxepine
8.875
0.99
1.50
1.69
15
2-Heptenal
9.733
3.08
2.55
3.82
16
Benzaldehyde
9.892
0.88
2.71
2.50
17
5-Hepten-2-one
10.967
2.58
9.37
6.14
18
2-pentyl-Furan
11.092
2.13
3.23
1.75
19
Octanal
11.592
1.11
15.16
1.49
20
2-methyl-6-methylene-2-Octene
13.775
5.67
0.73
10.96
21
Heptane
14.075
0.82
8.02
5.35
22
Nonanal
16.075
2.28
1.15
1.21
23
Decanal
20.767
12.93
1.51
1.46
24
Dodecamethyl Cyclohexasiloxane
26.425
5.20
0.36
0.82
25
Tetradecamethyl Cycloheptasiloxane
33.650
0.85
ND
0.78
26
Hexadecaethyl Cyclooctasiloxane
40.167
0.92
ND
ND
27
Ni
51.432
1.63
ND
ND
Ni =not identified; ND = not detected
Figure 4: Per cent reduction in ESR signal intensity with Time.
0.00!
10.00!
20.00!
30.00!
40.00!
50.00!
60.00!
70.00!
80.00!
90.00!
100.00!
0! 5! 10! 15! 20! 25! 30! 35! 40!
Per!cent!reduction!(%)!
Time(Days)!
1kGy!
5kGy!
15kGy!
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